[Toán 8] Toán đại số 8

T

transformers123

$\dfrac{2007}{-x} < 2008$

$\iff \dfrac{2007}{x}+2008 > 0$

$\iff \dfrac{2008x+2007}{x} > 0$

$\iff \begin{bmatrix}\begin{cases}2008x+2007 > 0 \\ x > 0\end{cases}\\\begin{cases}2008x+2007 < 0 \\ x < 0\end{cases}\end{bmatrix}$

$\iff \begin{bmatrix}\begin{cases}x >
\dfrac{-2007}{2008} \\ x > 0\end{cases}\\\begin{cases}x < \dfrac{-2007}{2008} \\ x < 0\end{cases}\end{bmatrix}$

$\iff \begin{bmatrix}x>0 \\x < \dfrac{-2007}{2008} \end{bmatrix}$

Kết luận là xong :D
 
P

phamhuy20011801

$\frac{2007}{-x}<2008$
\Leftrightarrow $\frac{-2007}{x}-2008<0$
\Leftrightarrow $\frac{-2007-2008x}{x}<0$
\Leftrightarrow ...
 
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